Air seeder blockage monitoring system

ABSTRACT

A particle blockage monitoring system employs a flexible piezoelectric particle sensor element in a portion of a particle flow path so that a number of particles traveling in the particle flow path strike the flexible particle sensor element while preventing damage to the particles and maintaining the forward momentum of all the particles in the particle flow path. In order to provide flexibility in monitoring particles of different types and to increase the information rate, the use of a one-shot multivibrator to temporarily store a particle detection signal as in the prior art is avoided. Also, serial sampling of the particle sensor data is avoided to increase the information rate. Instead, a comparator that includes a diode in a feedback loop so as to function as a latch is used in conjunction with a serial shift register that has parallel data input lines. This enables a microprocessor to monitor the output from a multiple-bit memory element which stores a digital representation of the outputs of plural sensor elements at a higher rate than attainable in the prior art. As a result of the increased rate at which information can be obtained from the particle sensor elements, the microprocessor can not only provide particle flow blockage status data but can also provide particle flow rates for the monitored particle flow paths.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 08/883,853filed Jun. 27, 1997, entitled "Air Seeder Blockage Monitoring System",which application was a continuation-in-part of U.S. application Ser.No. 08/855,625 filed May 14, 1997, entitled "Method and Circuit forDetermining if Seed Sensor is Operably Connected to Seed MonitorSystem".

BACKGROUND OF THE INVENTION

Prior art seed blockage monitoring systems typically employ a seed flowdetector comprising a pin which extends into the seed flow path. The endof the pin is fixed to one face of a ceramic piezoelectric transducer.Seeds flowing in a seed path impact the pin, causing the piezoelectrictransducer to undergo a strain. The signals generated by thepiezoelectric transducer are detected and interpreted as signalsgenerated by seeds flowing in the seed flow path. Examples of this typeof monitoring system are U.S. Pat. No. 5,177,470 to Repas, and U.S. Pat.No. 4,441,101 to Robar. One problem with this type of sensor is that theintrusion of the pin into the seed flow path can itself be the cause ofseed flow blockage.

Another type of piezoelectric sensor is disclosed in U.S. Pat. No.4,238,790. In this patent, a metal plate 16 (FIG. 2) located within aconduit is struck by seeds as they pass down the conduit. The impact ofthe seeds on the plate strains a piezoelectric crystal to which theplate is affixed, which in turn generates signals indicative of seedflow. A problem associated with this type of sensor is that the strikingof the hard metal plate may damage the seeds. Further, because themomentum of the seed must affect the entire mass of the rigid platebefore imparting a strain in the piezoelectric crystal, the sensorsensitivity is low.

In U.S. Pat. No. 4,491,241 to Knepler et al., piezoelectric sensors 10,12 (of undisclosed design) emit an electrical signal when struck by aseed. The electrical signal is input to a one-shot circuit 36 (FIG. 2),which functions as a one-bit memory to store the seed pulse for a perioddetermined by a capacitor 42. A respective sensor circuit 14, 16(FIG. 1) is coupled intermediate each of the sensors 10, 12 and a commonsignal line 18. The sensor circuits 14, 16 are coupled in seriescircuit, with the first sensor circuit 14 connected to an enable line 20and the last sensor being connected to a termination circuit 17. Thecommon signal line 18 and the enable line 20 are each coupled at one endto a monitoring and control circuit 22. This circuit includes a clocksignal generator and a counter. The monitoring and control circuit 22also drives an alarm indicator 24 (FIG. 11A) and a visual display 26(FIG. 1) and indicates to the operator when a particular sensor hasfailed to detect seeds.

In operation, the sensor circuits are enabled sequentially by a signalapplied to flip flop 30 (FIG. 2) on enable line 20 from the monitoringand control circuit 22. Flip-flops 30 and 32 operate jointly to enablethe gate 34 to pass sensor data from one-shot circuit 36 to commonsignal line 18 and, as well, to generate an enabling signal to the nextsensor circuit in the series connection after the initial interrogationof the gate 34. If, at the time the one-shot circuit 36 is interrogated,the output therefrom indicates that seeds are being dispensed, a logic 1signal is placed on the common signal line 18. If no seeds are beingdispensed, a signal level intermediate a logic 1 and a logic 0 is placedon the common signal line 18. The monitoring and control circuitdiscerns the intermediate level signal and displays that a seeddispensing fault has occurred at a particular sensor location indicatedon a counter 98 (FIG. 3A).

Upon the last sensor in the series connection being interrogated, thetermination circuit 17 receives the enable signal, which has been passedalong from one sensor circuit to the next in bucket brigade fashion aseach is interrogated. The termination circuit, in response to receivingthe enable signal, places a logic 0 on the common signal line 18. Thelogic 0 on the common signal line 18 causes the monitoring and controlcircuit 22 to reset the counter 98. Should a failure occur in thetermination circuit 17 or related components, the counter will continueto count upwardly, thus triggering a failure signal and an alarm.

One disadvantage with the system disclosed in Knepler et al is that,once the one-shot has detected a seed being dispensed, another seed cannot be detected until the one-shot has reset itself As the period ofeach one-shot is determined by the value of the capacitor 42, thisperiod can not readily be adjusted.

In the embodiment illustrated in FIG. 6 of Knepler et al, amicroprocessor is employed to scan the circuits 14,16, etc. at apreferred rate of 10 kHz(see column 1 1, line 31). This overcomes adelay in scanning encountered when using the prior embodiment. In thatembodiment, when a failure signal is detected, scanning is suspendedfrom one-half to one second while a display of the number of the failedunit is activated (see column 10, line 23).

Although use of a microprocessor allows more rapid scanning of thesensor circuits 14,16, etc., the fundamental limitations of thecircuitry, as discussed above, still exist. Thus, even in thisembodiment the one-shot retains the seed strike information forapproximately 34 ms (see column 16, line 41). Therefore, increasing rateof the interrogation beyond about 30 times per second (the inverse of 34ms) accomplish nothing, since there is no new information to be obtaineduntil the one-shots have reset themselves.

Another disadvantage of the circuitry in Knepler et al is that atermination circuit 17 is required to make the system operable; shouldthe termination circuit 17 fail, the entire system becomes inoperable.

A final disadvantage of all the prior art seed blockage monitoringsystems known to applicant is that the piezoelectric elements areceramic elements. The ceramic element undergoes a strain when a hard,inflexible surface or pin that is attached to the ceramic element isstruck by a seed. This has the disadvantages of the seed possibly beingdamaged by striking the hard surface or pin, and the sensing not beingas sensitive as it could otherwise be. Since the entire mass of therigid pin or plate must be affected before causing a strain (i.e.,output signal) in the piezoelectric element, the sensitivity is reduced.For this reason, the prior art systems are not well adapted to detectingvery small seeds.

Also, the prior art seed blockage monitoring systems are subject toerror resulting from induced noise, as may result from static chargebuildup/discharge on the seed planter equipment or from other inducedvoltages resulting from electromagnetic fields.

Finally, the prior art seed blockage monitoring systems are not easilyadapted to different seed monitoring configurations. For instance, itmay be desired to operate with only one sensor connected per header (oneexample of what will be called herein as a "partial-run" configuration)in order to monitor for a primary seed tube blockage, thereby reducingthe overall cost of the seed blockage monitoring system to a minimum.Or, it may be desired to operate with each secondary seed tube havingits own sensor (herein termed a "full-run" configuration) so as to beable to monitor blockage of all the primary and secondary seed tubes.Prior art seed blockage monitoring systems are not well-suited tooperating in both a "partial-run" and a "fill-run" seeding operation.

BRIEF SUMMARY OF THE INVENTION

A first object of the present invention is to provide a piezoelectricsensor element that is relatively soft and pliable rather than rigid, sothat seeds are not damaged when they impact onto the sensor and so thatthe sensor is more sensitive, thus enabling smaller seeds to be detectedby requiring less momentum transfer in order to detect a seed.

A second object of the invention is to minimize the intrusion into theseed flow path by the sensor. This is accomplished in part by the designof the sensor, which makes it more sensitive, and in part by the mannerin which the sensor is mounted in the seed flow path. The decrease ofthe intrusion of the sensor into the seed flow path has two advantages.It reduces the possibility that seeds will be damaged as they strike thesensor, and almost eliminates the possibility that a sensor element willcause a seed flow blockage.

A third object of the invention is to increase the rate that informationmay be obtained from the piezoelectric sensors, thereby enabling aparticle blockage monitor to also provide information as to the actualnumber of particles flowing in various monitored particle flow paths aswell as information as to the relative rates of particle flow.

A fourth object of the invention is to eliminate the need to employ atermination circuit 17 as employed in U.S. Pat. No. 4,491,241.

A fifth object of the invention is to provide circuitry wherein thememory period of an impact event (hereinafter termed "seed event", inview of the immediate applicability of the invention to determining seedblockage) can be readily adjusted.

A sixth object of the invention is to provide circuitry wherein datafrom multiple sensor memory units can be simultaneously read and reset,thereby enabling higher data rates to be achieved than in the prior art.

A seventh object of the invention is to decrease the possibility thatdischarges from static build-up, or from other electromagnetic fields,may affect the operation or accuracy of a blockage monitor, especially aseed blockage monitor.

The present invention will be more fully understood from the detaileddescription and accompanying drawings, which are given by way ofillustration only, and thus, are not limitative of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a tractor towing an air seeding systemincluding a blockage monitoring system according to an embodiment of thepresent invention;

FIG. 2 is a cut-away side view of the blockage monitoring system of thepresent invention in association with the air seeding system of FIG. 1;

FIG. 3 shows a top view of a "full-run" air seeder blockage monitoringsystem;

FIG. 4 shows a top view of a "partial-run" air seeder blockagemonitoring system;

FIG. 5 is a perspective view of a fully assembled blockage sensor unit;

FIG. 6 shows an exploded view of the blockage sensor unit of FIG. 5;

FIG. 7A is a view of the top of a flexible piezoelectric sensor elementused in the invention;

FIG. 7B is an exploded side view of the same sensor element as shown inFIG. 7A;

FIGS. 8A-8C show top, side cross-sectional and perspective views,respectively, of a blockage sensor unit cover;

FIGS. 9A-9C illustrate the blockage sensor unit, with FIG. 9A being atop view and FIGS. 9B and 9C being respective side views of twodifferent embodiments that do not differ in top view but differ in theirside views;

FIG. 10 is an exploded view of a slave unit enclosure;

FIG. 11 is a schematic diagram illustrating the circuitry in the variousslave units and the connections between the blockage monitoring unit andthe various slave units;

FIG. 12 is a schematic diagram illustrating the circuitry contained in ablockage monitor unit or slave unit to interface to a piezoelectricsensor;

FIG. 13 is a diagram of one example of framing and input bits that maybe used when employing 16 bit, parallel input, serial output, shiftregisters in accordance with the invention as illustrated in FIG. 11;and,

FIG. 14 is a display of the hit data and status of the sensorsassociated with a particular header.

DETAILED DESCRIPTION

FIG. 1 shows a side view of a tractor 20 intended to represent varioustypes of farm tractors that perform various tasks in a high volumeagricultural environment as may be present on a farm. In the depictionof FIG. 1, the tractor 20 is towing an air seeding system 22, includinga tool bar 24 and an air cart 26, by a tow bar 28. The air seedingsystem 22 can be any known air seeding system, such as the 735 AirSeeder and 737 Air Hoe Drill, both available from the John DeereCompany.

The tool bar 24 creates multiple parallel furrows in the soil of a fieldarea to be planted, dispenses a controlled quantity of seeds into thefurrows, and then covers the furrows in a manner that allows the seedsto germinate and then become plants. Known air seeding systems such asthe air seeding system 22 can simultaneously plant up to ninety-six rowsof seeds. The configuration of the tool bar 24 and the air cart 26 canbe reversed in that the tractor 20 can tow the air cart 26 and the aircart 26 can tow the tool bar 24.

FIG. 2 shows a cut-away, side view of a portion of the air seedingsystem 22. The air cart 26 (FIG. 1) includes a hopper 30 that holds aquantity of a particulate matter to be dispensed by the air seedingsystem 22. The hopper 30 can hold any particulate matter for thepurposes described herein, such as various grains, seeds, fertilizers,and herbicides. For the purposes of this discussion, the air seedingsystem 22 will be described as dispensing seeds 32 of any suitable type.The flow of seeds 32 from the hopper 30 is controlled by a rotarymetering system 34. The controlled flow of seeds 32 from the meteringsystem 34 distributes the seeds 32 into a primary manifold 36 through asuitable conduit 38. A plurality of primary seed tubes 40, one of whichis shown in FIG. 2, are connected to the primary manifold 36 to receivethe flow of seeds 32 from the hopper 30. For the embodiment of the airseeding system that seeds ninety-six rows, there would be eight primaryseed tubes 40.

A fan 42 is connected to the primary manifold 36 by a hose 44. The fan42 provides air pressure to the primary manifold 36 so as to cause theseeds 32 to move through the primary manifold 36 into the primary seedtubes 40 under air pressure. Each primary seed tube 40 is connected to aseparate secondary manifold, commonly referred to as a header 46. Aplurality of secondary seed tubes 48 are connected to each of theheaders 46. In the embodiment being discussed herein, there are twelvesecondary seed tubes 48 connected to each header 46. Each secondary seedtube 48 is connected to an opener 50. The opener 50 can be a bladedevice that creates furrows in the soil being planted from the motion ofthe tool bar 24 such that the seeds 32 are dispensed from the opener 50at the appropriate depth into the soil. Ground closers 52, depicted inFIG. 1, then close the furrows to cover the seeds 32 with soil. Ablockage monitor unit 54, is attached to the tool bar 24 in closeproximity to one of the headers 46. A blockage sensor unit 56 isattached to the secondary seed tube 48.

One preferred embodiment of the air seeder blockage monitoring system,referred to as a "full-run" air seeder blockage monitoring system, isdepicted in FIG. 3. A "full-run" air seeder blockage monitoring systemis defined as one in which every connected secondary seed tube 48 in thesystem is fitted with an individual blockage sensor unit 56, such thatblockage can be detected if it occurs in any of the primary seed tubes40 or in any of the secondary seed tubes 48 which are connected to thesystem.

FIG. 3 shows a top view diagram of the "full-run" air seeder blockagemonitoring system. For clarity, the diagram has been simplified suchthat elements of the system which can be plural in nature may appear insingular or in a limited representation of their true number. The seeds32 are carried by a plurality of primary seed tubes 40 to a number ofheaders 46, located on the tool bar 24. The headers 46 distribute theseeds 32 through a plurality of secondary seed tubes 48 (e.g., twelvesecondary seed tubes per header). Blockage sensor units 56 are insertedin the secondary seed tubes 48.

The processing hardware for the "full-run" air seeder blockagemonitoring system is located within the blockage monitor unit 54. Theblockage monitor unit 54 is housed in a rugged enclosure (e.g., JohnDeere wedge box) and contains a microprocessor 60 (not shown in FIG. 3)or other signal processing means by which to analyze sensor data. Theblockage monitor unit 54 is linked to a display area by a common databus 58, such as CAN or SAE J1850B. Two serial interface links 62 and 62Aare used to send signals and receive data from auxiliary data collectionunits, referred to as slave units 64. The serial interface links 62 and62A are four wire interconnects that link a plurality of slave units 64with the blockage monitor unit 54 in a serial manner (referred tohereinafter as a daisy chain configuration).

Each header 46 in the "full-run" air seeder blockage monitoring system(other than the header monitored by the blockage monitor unit 54) may beequipped with one slave unit 64, such that all of the blockage sensorunits 56 associated with the secondary seed tubes 48 for a particularheader 46 are interfaced to the associated slave unit 64 by suitablesensor wire cable harnessing 66 (e.g., 22 AWG stranded, twisted pairwith PVC insulation). Or, as illustrated in FIGS. 3 and 4, one or moreblockage sensor units 56 may be connected directly to the blockagemonitor unit 54. In this case, the blockage sensor units 56 connected tothe blockage monitor unit 54 are interfaced through the sensor interfacecircuit 162 (FIG. 12) to digital inputs of the microprocessor 60. In analternative embodiment, the analog sensor signals of thedirectly-connected sensor units 56 are input to analog inputs of themicroprocessor 60. The main harnessing that provides power to monitorunit 54 also contains sensor wire cable harnessing 66, allowing it toconnect directly to a plurality of blockage sensor units 56 associatedwith the secondary seed tubes 48 of one of the headers 46.

Each slave unit 64 is housed in a special enclosure (FIG. 10) whichincludes within the enclosure circuitry (FIG. 12) which filters,amplifies, and converts analog signals received from the blockage sensorunits 56 into a digital format. The digital format signals from variousblockage sensor units 56 are then serially transmitted to the blockagemonitor unit 54 (FIG. 11) by using a serial shift register havingparallel data input ports or by other equivalent structure for thepurpose intended, such as by using a microprocessor.

An alternate, cost-reduced embodiment of the air seeder blockagemonitoring system, referred to as a "partial run" air seeder blockagemonitoring system, is depicted in FIG. 4. A "partial run" air seederblockage monitoring system is defined as one which has been mainlydesigned to detect blockage of the primary seed tubes 40.

FIG. 4 shows a top view diagram of one example of a "partial-run" airseeder blockage monitoring system. For clarity, the diagram has beensimplified, such that elements of the system which can be plural innature may appear in singular or in a limited representation of theirtrue number. The seeds 32 (FIG. 2) are carried by a plurality of primaryseed tubes 40 to a number of headers 46, located on the tool bar 24. Theheaders 46 distribute the seeds 32 through a plurality of secondary seedtubes 48 (e.g., twelve secondary seed tubes per header). Blockage sensorunits 56 are inserted in a representative sample set of the secondaryseed tubes 48 associated with each header 46 (e.g., one blockage sensorunit per header).

The processing hardware and software for the "partial-run" air seederblockage monitoring system is located within the blockage monitor unit54. The blockage monitor unit 54 is housed in a rugged enclosure (e.g.,John Deere wedge box) and contains a microprocessor 60 (not shown inFIG. 4) or other signal processing means by which to analyze sensordata. The blockage monitor unit 54 is linked to a display area by acommon data bus 58, such as CAN or SAE J1850B. Two serial interfacelinks 62 and 62A are used to send signals and receive data fromauxiliary data collection units, referred to as slave units 64. Theserial interface links 62 and 62A are four-wire interconnects that linka plurality of slave units 64 with the blockage monitor unit 54 in adaisy chain configuration.

Each header 46 in the "full-run" air seeder blockage monitoring system(other than the header monitored by the blockage monitor unit 54) may beequipped with one slave unit 64, such that all of the blockage sensorunits 56 associated with the secondary seed tubes 48 for a particularheader 46 are interfaced to the associated slave unit 64 by suitablesensor wire cable harnessing 66 (e.g., 22 AWG stranded, twisted pairwith PVC insulation). Or, as illustrated in FIGS. 3 and 4, one or moreblockage sensor units 56 may be connected directly to the blockagemonitor unit 54. In this case, the blockage sensor units 56 connected tothe blockage monitor unit 54 are interfaced through the sensor interfacecircuit 162 (FIG. 12) to digital inputs of the microprocessor 60. In analternative embodiment, the analog sensor signals of thedirectly-connected sensor units 56 are input to analog inputs of themicroprocessor 60. The main harnessing that provides power to monitorunit 54 also contains sensor wire cable harnessing 66, allowing it toconnect directly to a plurality of blockage sensor units 56 associatedwith the secondary seed tubes 48 of one of the headers 46.

For "partial-run" systems, it should be noted that other configurationsof electronic control box arrangements are feasible. For example: allsensors 56 could plug into the blockage monitor unit 54, thus obviatingthe need for any slaves; or, more than two sensors could be plugged intothe blockage monitor unit 54 and each slave unit 64.

FIG. 5 shows an isometric view of the fully assembled particle blockagesensor unit 56 and FIG. 6 shows an exploded view of the particleblockage sensor unit 56. In this embodiment of the particle blockagesensor unit 56, seeds 32 pass through a secondary seed tube 48 and enterthe blockage sensor unit 56. Some of the seeds 32 impinge on a flexiblepiezoelectric sensor element 68, such as piezoelectric film. When a seed32 impinges on the flexible piezoelectric sensor element 68, thepiezoelectric effect generates a voltage, which is transmitted either toone of the slave units 64 and then to the blockage monitor unit 54, orto the blockage monitor unit 54 directly, and is interpreted as a "seedevent".

The flexible piezoelectric sensor element 68 (FIG. 7A) is commerciallyavailable from AMP Incorporated. As shown in the exploded, side view ofFIG. 7B, MYLAR sheeting 70, 70A sandwiches silk-screened, silver inklayers 71B and silk-screened piezoelectric material 71C, with layers 71Abeing adhesive layers. A second piece of MYLAR sheeting 70A may bebonded in place over the top of the piezoelectric material to act as aflexible protective covering. Two solder-type connectors 72 and 72A arecrimped into place at the base of the flexible piezoelectric sensorelement 68 and connected to suitable sensor wire cable harnessing 66(e.g., 22 AWG stranded, twisted pair with PVC insulation) equipped witha connector body 73 (such as connectors commercially available fromPackard Delphi) having female terminals. Alignment holes 74 and 74Ainsure that the flexible piezoelectric sensor element 60 is alignedcorrectly when it is installed into a blockage sensor cover 76 (shown indetail in FIGS. 8A-8C).

The blockage sensor cover 76 can be made of an injection moldedthermoplastic material such as a polycarbonate/ABS blend. The flexiblepiezoelectric sensor element 68 (FIG. 7A) is designed such that thealignment holes 74 and 74A fit directly over alignment pins 78 and 78A(shown in cross-section in FIG. 8B) in the blockage sensor cover 76.This allows the sensing area of the flexible piezoelectric sensorelement 68 to be aligned directly upon the angled portion of theblockage sensor cover 76, referred to as an angle of intrusion α. Theillustrated angle α is an angle of approximately, but not limited to,thirteen degrees. (This angle, illustrated in FIG. 9B, may alternativelybe measured from the intrusion surface normal to a direction that isnormal to the flow axis of seeds in blockage sensor unit 56. A thirteendegree angle of intrusion reduces the cross-sectional area of thesecondary seed tube 48 by no more than seven percent, yet allows seeds32 to effectively impact the flexible piezoelectric sensor element 68while not being slowed significantly in their travel along the seedtube.

Referring to FIG. 8A, an air gap 82 is designed into the blockage sensorcover 76 directly behind the sensing area of the flexible piezoelectricsensor element 68. This air gap 82 effectively increases the sensitivityof the flexible piezoelectric sensor element 68 (by allowing strain inthe flexible piezoelectric sensor element to occur freely) so that evensmall seeds, such as canola, can create a piezoelectric- effect outputfrom the sensor.

A directional arrow 84 appears in the isometric view of the blockagesensor cover 76 in FIG. 8C. This directional arrow 84 has been added tothe design as an aid in correctly placing the blockage sensor unit 56into the secondary seed tube 48 at the time of installation. Thedirectional arrow 84 is to point following the direction of seed flowfrom the header 46, through the secondary seed tube 48, to the opener50. The inner surface edge 87 of the blockage sensor cover 76 has beenprepared in such a manner that it can be fitted directly onto a blockagesensor tube 86 (FIG. 9) and welded ultrasonically into place. Theblockage sensor cover 76 is designed to include a means of tensionrelief 88 for the sensor wire cable harnessing 66, which is set in placeduring the ultrasonic welding operation.

FIGS. 9A-9C illustrate the blockage sensor unit. FIG. 9A shows a topview of two alternate embodiments of the blockage sensor tube 86 thathave an identical top view. FIGS. 9B and 9C are side views thatillustrate the differences between the two alternate embodiments. Theblockage sensor tube 86 can be made of an injection molded thermoplasticsuch as a polycarbonate/ABS blend. The blockage sensor cover 76 (FIG. 8)is designed such that the pins 78 and 78A fit into correspondingimpressions 90 and 90A in the blockage sensor tube 86. In the firstembodiment,as illustrated in FIG. 9B, the flexible piezoelectric elementis generally planar in shape. The angle of intrusion α of the intrusionsurface 80 upon which the flexible piezoelectric sensor element 68 isfastened matches the angled slope 92, which is inclined at the angle ato a central axis of the secondary seed tube. The sensor area cutout 94exposes the sensing area of the flexible piezoelectric sensor element 68to the seeds 32 (FIG. 2) flowing through the secondary seed tube 48.Thus, a small portion of the seeds flowing in the seed flow path strikethe flexible piezoelectric sensor.

Because it is believed that a velocity gradient of particles within thetube exists wherein, for example, seeds nearer the center of the tubehave a higher velocity as a result of increased air velocity propellingthem near the center of the tube, it may be desirable to form theflexible sensor surface into an arcuate shape, wherein the angle ofintrusion decreases towards the sensor end nearest the center of thetube. Such as design is illustrated in FIG. 9C. This would appear tohave an advantage in that a more constant amount of momentum istransferred to the sensor, resulting in a more uniform sensitivity ofdetection across the sensor surface as well as reduced risk that thepresence of the sensor intruding into the tube will itself contribute toa blockage. The arcuate shape removes a more nearly constant amount offorward momentum from a seed, irrespective of a velocity gradient withinthe seed tube.

A combination of factors lead to advantageous results when using thepresent sensor arranged in the manner illustrated. First, because theimpact object is a flexible MYLAR sheet as opposed to an inflexibleplate or pin, as in the prior art, the amount of strain induced in thepiezoelectric detector for a given seed impact is higher than in theprior art. This results in the piezoelectric sensor being moresensitive, and allows very small seeds, such as canola, to be monitoredwith the present monitoring system. Second, the higher sensitivitydetector also allows the intrusion angle of the sensor into the flowpath to be reduced. This results in only a slight change of momentum formost seeds that strike the flexible MYLAR surface of the sensor, andvirtually eliminates any seeds from being damaged. By minimizing thechange in momentum needed to detect seed flow, the forward momentum ofall the seeds in the seed path is maintained to a greater extent thanwith prior art systems. Thus seed blockages, caused by the seed blockagesensor being in the path of the seeds, are minimized.

The outer surface edge 96 of the blockage sensor tube 86 (i.e., thatwhich is complementary to the inner surface edge 87 of the blockagesensor cover 76) has been prepared in such a manner that the blockagesensor cover 76 (FIGS. 8A-8C) can be directly welded into placeultrasonically. Both ends of the blockage sensor tube 86 have anincreased internal and external diameter in comparison to its centerportion. The increase in diameters of the ends conform to the thicknessof the secondary seed tube 48, forming acceptors 98 and 98A (FIG. 9A).Ends of the secondary seed tubes 48 are inserted into acceptors 98 and98A. The portions of the secondary seed tubes 48 and the attachedblockage sensor tube 86 that constrain the seeds have identical internaldiameters so that a smooth flow path boundary is achieved. Acceptor 98contains two fastener holes 100, 100A and acceptor 98A contains twofastener holes 100B, 100C. Metal spring clips 102 and 102A (FIG. 5 andFIG. 6), fit into these holes so as to secure the connection of theblockage sensor tube 86 to the secondary seed tube 48.

FIG. 10 shows an exploded view of the preferred embodiment of the slaveunit enclosure 104. The slave unit enclosure top 106 can be made of aninjection molded thermoplastic such as a polycarbonate/ABS blend. Theslave unit enclosure 104 is uniquely designed to house the circuitry andto provide multiple connector ports 108 for the sensor wire cableharnessing 66 (FIG. 6). Two serial interface ports 110 and 110A aredesigned for serially linking the slave units 64 and for communicatingwith the blockage monitor unit 54. Three mounting holes 112, 112A, and112B are provided.

The slave unit enclosure bottom 114 can be made of an injection moldedthermoplastic such as a polycarbonate/ABS blend. Four screw holes 116are provided for screws to fasten the slave unit enclosure bottom 114 tothe slave unit enclosure top 106. A partial block insert 118 can be madeof an open cell urethane with a protective film or of a closed cellurethane. The partial block insert 118 is used to close extraneousconnector ports 108 when the circuitry has been depopulated for use inthe "partial-run" air seeder blockage monitoring system. Oralternatively, the holes can be plugged by molded plastic using aninsert into the molding tool.

FIG. 11 is a schematic diagram illustrating the circuit connectionsbetween the blockage monitor unit 54 and various slave units 64. Forclarity, FIG. 11 has been simplified, such that only one serialinterface link is represented. It is to be understood that other serialinterface links may be utilized in the same manner. Each of the serialinterface links 62 and 62A (illustrated in FIG. 3)are clocked separatelyby the microprocessor 60. Although a plurality of slave units 64 areunderstood to exist, only two slave units 64 are represented in theschematic diagram of FIG. 11, each functioning in the same manner. It isalso to be understood that the microprocessor 60 of the blockage monitorunit 54 directly monitors a plurality of blockage sensor units 56 (notshown)through the sensor interface circuit 162 from one header 46.

In FIG. 11, the blockage monitor unit 54 contains the microprocessor 60,(e.g., Siemens C167 series) and associated circuitry. A driver line 120of a serial interface link is shown exiting the microprocessor. Thedriver line 120 carries the clock signal 122 to each of the slave units64. The blockage monitor unit 54 communicates with all of the slaveunits 64 connected to the driver line 120 via pulses of the clock signal122. Each slave unit 64 receives the pulses of clock signal 122 in arespective shift register 132 and responds by serially transmitting anystored digital signals in the form of bits back to the blockage monitorunit 54 via the receiver line 126.

Within the driver line 120, the clock signal 122 is used to perform anumber of different signaling functions: signaling when the slave unit64 should capture data, when it should clear stored data, and when itshould perform sensor detection (see timing diagram at the top of FIG.11). When the clock signal 122 is driven high, a latch/load signal 128is created in the latched state by a positive peak detector 130. Thehigh level of the latch/load signal 128 is then detected and held whilethe clock signal 122 is switching and slightly longer. This latches thebits in the serial shift register 132 so that they aren't cleared duringthe clock signal 122 shifting. The serial shift register 132 of a givenslave unit 64 has a plurality of sensor data input lines 133, whichreceive the digital signal output 148 (see FIG. 12) as bits from thesensor interface circuit 162.

As shown in FIG. 11, there is provided a shift register 132 for eachrespective slave unit 64, and the shift registers are connected inseries. A clock signal 122 is fed to each shift register so as to shiftthe data in each shift register. In the preferred embodiment, the datafrom each register that is shifted (in a serial fashion) into theblockage monitor unit 54 consists of up to 12 data input lines 133. Atotal of 16 bits are shifted to the blockage monitor unit 54 by eachslave unit 64, of which 12 data bits are from sensors and the other 4are framing bits to maintain data integrity. When the latch/load signal128 drops to its low level again, it enables the load function so thatnew data can enter the serial shift register 132. Therefore, the rising(see FIG. 13) edge of the clock signal 122 enables the transition fromthe open state to the latched state. Also, at the rising edge of theclock signal 122 an active low one shot 134 generates the clear signal136 that clears the latched comparator 144 to allow new seed events tobe captured. When the clock signal 122 is driven high and held for anextended period of time, the negative peak detector 158 is allowed totime out and drive the sensor detect signal 156 high. This signal isused in the sensor interface circuit 162 to determine which sensors areattached to the slave.

FIG. 12 is a schematic diagram illustrating the circuitry within ablockage monitor unit 54 or slave unit 64 to interface to apiezoelectric sensor. The flexible piezoelectric sensor element 68generates an analog signal at the occurrence of a seed event. In apreferred embodiment, a bandpass filter 138 and an amplifier 140 areprovided, however, these two items can be omitted or their orderinterchanged. In the preferred embodiment, the analog signal from asensor first passes through a bandpass filter 138 and than an amplifier140. Then it is compared to a reference voltage 142. If the analogsignal exceeds the level of the reference voltage 142, it will changethe state of the output comparator 144 to the open state which is thenpulled high by resistor 149. A diode feedback 146 latches the outputcomparator 144 such that, as soon as the digit signal output 148 tripshigh, it stays high. The clear signal 136 travels through diode 154 andforces the positive input of the output comparator 144 low in order toenable it again. The clear signal 136 returns high such that, as soon asnew seed events are received, the comparator 144 (which serves as alatch) i.e., a unit bit memory element) is enabled to capture theseevents.

The sensor detect signal 156 is used to determine whether apiezoelectric sensor is connected to the sensor interface circuit 162.Sensor detect signal 156 is generated and travels through an impedance,such as a capacitor 160, and into a sensor element interface line 163.If the flexible piezoelectric sensor element 68 is present, it reducesthe peak amplitude of the signal input to the comparator 144sufficiently that it doesn't trip the comparator 144. If the flexiblepiezoelectric sensor element 68 is not present, then the sensor detectsignal 156 will generate a peak voltage at the input to the comparatorsufficient to trip and latch the comparator 144 into a high state.

The microprocessor in the blockage monitor unit 54 monitors andtabulates the serial inputs received from the various shift registers132 (which each serve as a multiple bit memory element) of the slaveunits 64 as well as any inputs received directly from the sensorinterface circuitry 162 in the blockage monitor unit 54 so as to obtainthe total number of seed events within a given time period for eachsensor element 68.

FIG. 13 illustrates an example of the framing bits and input bits of a16 bit, parallel input, serial output, shift register which may beemployed as the shift registers in FIG. 11. (Of course, other shiftregisters, such as ones having 8 or 32 bit parallel inputs, etc., couldbe used depending on design choice and cost considerations.) In thepreferred embodiment, logic 1 framing bits are placed in bit positions 0and 15 by inputting a logical low signal to these parallel inputs of theshift register. Also, logic 0 framing bits are placed in bit positions 1and 14 by inputting a logical low signal to these parallel inputs of theshift register. This allows the microprocessor 60 to positivelydetermine the presence of the data from a slave unit 64. Also, byabsence of the framing bits, the absence or failure of a slave unit canbe inferred. Of course, these framing bits could also incorporate parityor other check bits to implement error detection or correction. Thus, a16 bit shift register allows 12 data bits to be placed simultaneouslyinto the register in bit positions 2-13. These data bits can then beclocked into the microprocessor of blockage monitor unit 54 by serialclock pulses 122 at a high rate.

As shown in FIG. 14, a display is provided which shows hit data and thestatus of the sensors associated with a particular header. Along theleft column is shown the sensors (R1-R12) attached to, in the caseillustrated, Header 1. In the second column are listed the hit data,corresponding to the number of particles detected by each sensor. In thethird column, is listed the particle flow status (e.g. "blocked", "notblocked") of a particle flow path associated with a respective sensorR1-R12, as well as the status of the sensor (e.g. "not present","disabled", "failed" or "ignored").

One advantage of the present invention over the prior art is that therate at which data can be obtained from the piezoelectric sensors ismuch higher. A high rate of monitoring for seed events in a blockagemonitoring system provides additional useful information to the operatorbesides the occurrence of seed blockages. For example, data as to therelative seed flow rates of the various flow paths can be displayed.

In addition, from empirical data (obtained by correlating the number ofdetected seed events for a given seed type versus the number of seedsthat actually flowed through the tube in the same period of time), theseed flow rate can be readily obtained by means of a look-up table, withthe inputs being seed type and number of detected seed events per givenperiod of time. Or, as an alternative, if one assumes that the seedspassing through the seed tubes are uniformly distributed, the number ofseeds passing through a seed tube can be determined by merelymultiplying the detected number of seed events and the inverse of theper cent intrusion of the flexible piezoelectric sensor into the seedtube cross-sectional area.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A particle blockage sensor system comprising:aparticle flow path having a cross-sectional area; a piezoelectric sensorelement having a flexible surface; and, means to support and align theflexible surface of said piezoelectric sensor element in the particleflow path, to thereby cause a number of particles flowing in theparticle path to impact said piezoelectric sensor element.
 2. Theparticle blockage sensor system of claim 1, wherein the particle flowpath cross-sectional area is reduced about seven percent by thepiezoelectric sensor element being supported therein.
 3. The particleblockage sensor system of claim 1, wherein the flexible surface of thepiezoelectric sensor element is arcuate in shape.
 4. The apparatus ofclaim 1, further including a slave unit connected to said piezoelectricsensor element, said slave unit comprising:means to output a binarysignal, responsive to an analog signal being generated by saidpiezoelectric sensor element when struck by a particle, indicative ofwhether a particle has struck the piezoelectric sensor element within agiven time period.
 5. The apparatus of claim 4, further including a bandpass filter and amplifier connected between said piezoelectric sensorelement and said means to output a binary signal.
 6. The apparatus ofclaim 1, further including a microprocessor connected to saidpiezoelectric sensor element so as to form a particle blockagemonitoring system.
 7. The apparatus of claim 6, wherein a slave unitmeans, which forms a binary signal indicative of whether a particle hasstruck said piezoelectric sensor element within a given time period, isconnected intermediate said microprocessor and said piezoelectric sensorelement in order to increase immunity of the particle blockagemonitoring system to noise.
 8. The apparatus of claim 6, and furtherincluding a display, wherein said microprocessor tabulates the number ofparticles detected by each piezoelectric sensor element over multipledata collection periods and displays on the display the number ofparticles detected by each piezoelectric sensor associated with aparticular header.
 9. The apparatus of claim 8, wherein saidmicroprocessor determines, from the number of hits detected by eachpiezoelectric sensor element over multiple data collection periods, aparticle flow status for a respective particle flow path associated witheach piezoelectric sensor element and displays said particle flow statusfor multiple particle flow paths on said display.
 10. The apparatus ofclaim 6, and further including a display, wherein said microprocessortabulates the number of particles detected from a piezoelectric sensorelement over multiple data collection periods, determines the number ofparticles per unit of time in the particle flow path associated with thepiezoelectric sensor element, and displays the results on said display.11. The apparatus of claim 10, wherein said microprocessor alsotabulates the number of particles flowing in all or selected ones ofmultiple particle flow paths, determines the total number of particlesflowing per unit of time, and displays the results on said display. 12.A particle blockage monitor system comprising:a microprocessor; one ormore particle sensor elements, each having a flexible surface whichprovides an output signal when struck by a particle; one or morecomparators, each having a positive and negative input and an output,one of said inputs of each comparator being connected to receive asignal representative of the output from a respective sensor element; afirst shift register having, as at least one data input, a signal outputfrom said one or more comparators; means to shift the data in the firstshift register serially into the microprocessor; and a second shiftregister connected in series to the first shift register, wherein themeans to shift data in the first shift register is connected to thesecond shift register so as to also shift data in the second shiftregister.
 13. A particle blockage monitor system comprising:amicroprocessor; one or more particle sensor elements, each having aflexible surface which provides an output signal when struck by aparticle; a plurality of unit-bit memory elements, each unit-bit memoryelement receiving an input from a respective particle sensor element andhaving an output; a multiple-bit memory element, capable of receivingand storing the respective outputs from said plurality of unit-bitmemory elements; and, means to serially transfer data contained in saidmultiple-bit memory element into said microprocessor.